1. Field of the Invention
The present invention relates to a temperature difference drive unit that acquires mechanical energy based on temperature fluctuation in the environment in which the drive unit is used and generates a drive force or electrical power from the mechanical energy. The invention also relates to an electric device, a timepiece and a light electrical appliance employing such a temperature difference drive unit.
2. Description of the Related Art
Mechanical timepieces such as wristwatches and pocket watches which are driven by mechanical energy accumulated in a main spring are widely in use. Some mechanical timepieces are of the manual-winding type whereby the main spring is wound by hand. Since this type of timepiece stops when the mechanical energy accumulated in the main spring is completely released, periodic winding of the main spring is required. Further, since the manual-winding mechanical timepiece no longer shows accurate time once it has stopped, the timepiece also has to be reset. Periodic winding and resetting of such a timepiece is inconvenient to the user.
Accordingly, a self-winding watch having a rotatably oscillating weight for automatically winding the main spring has been used. Since the main spring of the self-winding watch is automatically wound by movement of the watch, mechanical energy is accumulated in the main spring when the user wears the watch (e.g., on the wrist) during normal activity, so that the self-winding watch keeps moving without stopping under such conditions. However, such a self-winding watch stops accumulating energy in the mainspring when it is detached from the user""s wrist and placed at rest. If such a watch remains at rest too long, the mechanical energy stored in the main spring will be released and the watch will stop.
While the self-winding function is useful for wrist watches which can be moved during normal use, it is not applicable for timepieces, such as table clocks, that are intended to remain at rest. Accordingly, a table clock that obtains drive energy from a temperature change in the natural environment has been proposed. For instance, a table clock xe2x80x9cATMOSxe2x80x9d of Jaeger Lecoultre Co., Ltd. obtains drive energy from the temperature change in the natural environment using the expansion force of a material. Specifically, a phase change material in which the phase changes between gas and liquid at room temperature is accommodated in an expandable container, such that the main spring is wound as a result of the volume change of the phase change material which is caused by the temperature change. The clock is then driven by the mechanical energy accumulated in the main spring. The phase change material is a material whose phase changes between gas and liquid such as ammonia, carbon dioxide, alcohol and methyl chloride. Since the main spring of the clock has the capacity to store enough mechanical energy to continuously drive the clock for approximately seventy-two hours, enough mechanical energy can be stored in the main spring from the temperature changes that occur in an ordinary environment to prevent the clock from stopping in most circumstances, thus allowing semipermanent movement thereof.
However, since an electronic device such as a high accuracy electronic timepiece that employs a quartz oscillator cannot be driven by the above arrangement, there is another arrangement where a power generator is driven by the drive energy obtained by the temperature change (Japanese Patent Laid-Open Publication No. Hei 10-14265, Japanese Patent Laid-Open Publication No. Hei 6-341371). In this case, a phase change material whose phase changes between gas and liquid at room temperature is accommodated in an expandable container, as in the above-described table clock. A volume change of the phase change material caused by the temperature change is converted into a rotary drive force by a rack and the rotary drive force used to actuate the power generator. A prime mover such as a motor is driven by the electric power generated by the power generator to obtain the drive force for driving the timepiece.
In order for the rack to convert the volume change of the phase change material into the rotary drive force, the rack is fixed when the temperature continues to increase or decrease. When the temperature change reverses direction, the fixed rack is released as the phase change material rapidly and completely expands or contracts, thereby improving efficiency of converting electric power. Accurate time keeping can be maintained by installing a wave correction function into the timepiece.
There are certain disadvantages in using a phase change material that changes between the gas and liquid states to provide the initial source of energy. When the phase change material changes to gas, its thermal conductivity is significantly lowered, thus deteriorating resistivity to change in ambient temperature. Thus, the time from decrease in ambient temperature to volume reduction of the phase change material can be delayed. Accordingly, such a phase change material does not generate mechanical energy responsively in accordance with temperature difference, thus deteriorating conversion efficiency.
Further, since mixing different types of phase change materials whose phases change between gas and liquid results in a chemical reaction, the phase change temperature cannot be adjusted by mixing such different types of the phase change materials. As a result, the phase change material is contained in a variable volume container, where the internal pressure (i.e., the pressure applied to the phase change material) is increased by contracting the volume of the container in order to set the boiling point (phase change temperature) of the phase change material at a desired temperature.
Accordingly, such a container containing the phase change material is required to have a variable volume and be extremely airtight to avoid leakage of the high-pressure air to the outside, thus making production of the container difficult.
Further, since the above container contains the phase change material as a gas, a substantial amount of volume is required and a compressing means such as a strong spring is required in order to maintain the high pressure inside the container, so that size reduction of the whole device is difficult.
Moreover, since a phase change material has a prominently large expansion rate in changing between the gas and the liquid phases, a large pressure results when the phase change material is evaporated to saturated vapor, causing a large fluctuation in the pressure. Further, the high internal pressure to which the container is subjected, increases the likelihood that the container will experience mechanical fatigue, thereby making it difficult to manufacture a container having sufficient durability, thus further making production of the container difficult. While using a rigid and heavy container improves durability, such a container increases the size and weight of the device.
In the power generator described in the above-identified publications, since the fixed rack is released to intermittently generate power when the temperature change direction is reversed, the power generator is actuated many times when the temperature increase and decrease are repeated again and again within a short period of time.
Also, since the power cannot be efficiently generated until the power generator reaches a predetermined number of revolutions, drive energy is lost when the power generator is actuated many times within a short period of time, and is thus unable to sufficiently improve electric power conversion efficiency.
Further, in the aforesaid device, since number of revolutions of a rotor of the power generator is increased and decreased so that the voltage applied to the load of the power generator becomes constant, the rotor cannot be always rotated with the best power-generating efficiency. Therefore, the power-generating efficiency cannot be so improved and, since the available energy relative to the inputted thermal energy is decreased, energy utilization efficiency is likely to be deteriorated.
Also, the overall conversion process requires three conversions: a first conversion of thermal energy by the temperature difference into mechanical energy, a second conversion of the mechanical energy obtained in the first conversion into electric energy, and a third conversion of the electric energy obtained in the second conversion into mechanical energy. Since these conversions are performed sequentially and some energy is lost during each conversion, the final mechanical energy available energy relative to the inputted thermal energy is reduced, thus deteriorating energy utilization efficiency. Moreover, the reduced energy utilization efficiency makes it difficult to obtain electric power required for wave correction function, so that it is difficult to implement the wave correction function.
An object of the present invention is to overcome the above-mentioned problems.
Another object of the present invention is to provide a temperature difference drive unit for efficiently converting a temperature-change-based volume change of a material into electrical energy, and a electric device, a timepiece and a light electrical appliance incorporating such a drive unit.
According to one aspect of the present invention, a temperature difference drive unit is provided. Such a drive unit comprises a power generator driven by mechanical energy to generate electric power; and a mechanical energy generator for generating the mechanical energy supplied to the power generator, the mechanical energy generator comprising a thermal converter including a phase change material, the volume of which changes based on temperature at least in a temperature range in which the phase change material is in a solid-liquid phase, whereby the change in volume of the phase change material and the thermal converter is converted into the mechanical energy for driving the power generator.
The thermal conductivity of a substance drops significantly when it becomes a gas. For instance, air, ammonia and nitrogen dioxide have thermal conductivities of 0.024, 0.022 and 0.0145 W/(mxc2x7K) respectively. On the other hand, water and paraffin as a liquid and solid have thermal conductivities of 0.561 and 0.24 W/(mxc2x7K) respectively. Because the phase change material of the thermal converter does not become a gas within the operating range of the drive unit, the thermal conductivity of the thermal converter remains relatively high even after the phase change.
Accordingly, since superior thermal conductivity of the thermal converter can be obtained within an ordinary operating temperature range and superior resistivity to change in ambient temperature can likewise be obtained, the volume rapidly changes in accordance with temperature fluctuation, so that sufficient mechanical energy can be obtained in decreasing the ambient temperature, thereby improving conversion efficiency.
Further, many materials whose phase change between solid and liquid do not chemically react even when different type of such materials are mixed. Accordingly, the phase change temperature of the thermal converter can be adjusted by mixing the different compounds, without subjecting the inside of the container in which the thermal converter is contained to high pressure.
Moreover, since the inside of the container is not subjected to high pressure, the container need not be air tight at high pressure, the container is easier to manufacture. Also, with no internal high pressure, a compressing means such as a strong spring is not required, thus reducing the size of the whole device.
In the above temperature difference drive unit, the phase change material is preferably a mixture of compounds having different solid-liquid phase change temperature ranges, wherein the mixture ratio of the compounds is adjusted based on the environmental conditions in which the temperature difference drive unit is used to achieve desired operating characteristics.
By using a mixture of compounds as the phase change material, a thermal converter suitable for a particular temperature fluctuation range and speed of the use environment can be obtained, thus improving conversion efficiency.
In the above-described temperature difference drive unit, the thermal converter preferably further includes an additive for adjusting the solid-liquid phase change temperature range or volume-expanding characteristics of the phase change material. Accordingly, the solid-liquid phase change temperature range and volume-expansion characteristics of the phase change material can be adjusted by adding the additive, so that a thermal converter most suitable for the use environment can be securely obtained by adding the additive as necessary while checking the characteristics of the thermal converter after mixing the phase change material compounds.
In the above-described temperature difference drive unit, the mechanical energy generator may have a reciprocally-moving drive member driven by a volume change of the thermal to transfer the volume change inside the thermal converter container into externally usable mechanical energy, so that the power generator can be rotated by connecting a rack or the like to the drive member.
A gear train combining a plurality of gear wheels may be provided to transfer the mechanical energy of the drive member to the power generator. Since the thermal converter generates a large drive force as compared to a small volume change in changing between liquid and solid, the drive force of the thermal converter can be accelerated by the gear train by transferring the drive energy to the power generator through the gear train for more efficient generation of power.
The gear train is preferably set at a speed-increasing ratio for driving the power generator at a number of revolutions with a good power-generating efficiency. By so adjusting the speed-increasing ratio, even when the volume change of the thermal converter is slow, appropriate speed of the rotary drive force can be transferred to the power generator, so that the volume change of the thermal converter can be always efficiently converted into electric power, thus enhancing efficiency of the power generator.
The temperature difference drive unit may preferably have a mechanical energy accumulator for accumulating the mechanical energy generated by the mechanical energy generator. Since the drive energy generated by the volume change of the thermal converter is accumulated in the mechanical energy accumulator, the power generator can be continuously driven with the mechanical energy accumulator as a buffer, even when the temperature increase and decrease are repeated within a short period of time. Accordingly, the loss of drive energy caused by repeated actuation of the power generator within a short period of time can be avoided, thus sufficiently improving electric power conversion efficiency.
In the above temperature difference drive unit, the electric power generated by the power generator may preferably be supplied externally, the temperature difference drive unit being a power-generating unit. By arranging the temperature difference drive unit as a power-generating unit, the temperature difference drive unit can be used as a power supply of various timepieces and light electrical appliances.
The temperature difference drive unit may further have an elastic body as a mechanical energy accumulator for accumulating the mechanical energy generated by the mechanical energy generator, the elastic body being elastically deformed by a volume change of the thermal converter, and an elastic body controller for maintaining a displacement of the elastic body caused by the mechanical energy generator until the displacement of the elastic body reaches a predetermined value, and for releasing the displacement of the elastic body when the displacement of the elastic body exceeds the predetermined value.
By thus intermittently taking out the drive energy from the mechanical energy accumulator, the power generator can be continuously operated with great drive energy by accumulating a small drive energy generated by the volume change of the thermal converter within the mechanical energy accumulator, so that a power generator generating higher voltage and greater electric power than a conventional one can be used.
By providing the elastic body release, the elastic body can be quickly released as necessary to generate electric power, the handling of the temperature difference in drive unit can be improved. Further, since the manually operated elastic body release has a simple structure, the structure of the temperature difference drive unit is not so complicated and the size of the temperature difference drive unit is not so increased.
The electric power generated by the power generator of the temperature difference drive unit may preferably be supplied to a timepiece for measuring time or a light electrical appliance driven at low electric power.
By maintaining the above-described temperature drive unit relatively light and small, the size and weight of such a timepiece or light electrical appliance incorporating the drive unit is kept at substantially the same weight and size of the corresponding conventional arrangement.
Another object of the present invention is to provide a temperature difference drive unit capable of efficiently utilizing the thermal energy by the temperature change and an electric device having the same.
In another aspect, the present invention includes a mechanical energy converter for converting thermal energy obtained by change in ambient temperature into mechanical energy; a mechanical energy accumulator for accumulating the mechanical energy outputted by the mechanical energy converter; a rotor rotated by the mechanical energy; a power generator for generating an electric power in response to rotation of the rotor; a transfer unit for transferring the drive force of the rotating rotor to the power generator; and a controller, operated by the electric power from the power generator, for controlling the speed of the rotor.
In accordance with this aspect of the invention, since the mechanical energy accumulator works as a buffer even when the amount of the mechanical energy generated by the mechanical energy converter, the number of revolution of the rotor of the power generator does not greatly fluctuate.
By setting the number of revolutions in accordance with the highest conversion efficiency, the power generator can exert excellent conversion efficiency, thus utilizing the thermal energy with superior energy utilization efficiency.
The mechanical energy may preferably have a thermal converter whose volume or form changes in accordance with temperature change to generate mechanical energy by the change.
The thermal converter may either be a phase change material whose volume changes in accordance with a phase change caused by a temperature change or a form change material whose form changes in response to temperature change.
For instance, the phase change material may be those causing phase change between gas and liquid and between liquid and solid. The phase change material whose phase changes between gas and liquid may be ammonia, carbon dioxide and ethylene chloride. The phase change material whose phase changes between liquid and solid may be wax.
On the other hand, a form change material may be bimetal and shape memory alloy.
In order to enhance the efficiency of the temperature difference drive unit, a phase change material that does not change into a gas with extremely small thermal conductivity even after the phase change, i.e., the phase change material whose phase changes between liquid and solid, may preferably be used.
In the above temperature difference drive unit, the mechanical energy accumulator may preferably have an elastic body elastically deformed by the mechanical energy.
By accumulating the mechanical energy in the elastic body, the structure of the mechanical energy accumulator can be simplified and the size thereof can be reduced, thus reducing weight and size of the temperature difference drive unit.
In the temperature drive, the number of revolution may preferably be controlled to the predetermined number of revolution by adjusting an electric current flowing to the power generator to brake the rotor by an electric magnetic brake.
By braking the rotor with the electric magnetic brake generated by adjusting the electric current flowing to the power generator, energy consumption can be reduced for the braking unlike mechanical brake of the rotor, thus minimizing the energy required for controlling the number of revolution of the rotor, so that the thermal energy can be utilized with a superior energy utilization efficiency.
In the above, the transfer unit may preferably be a gear train combining a plurality of gear wheels, at least one of which is provided with an index for indicating time.
By using the temperature difference drive unit as a timepiece, semi-permanently driven timepiece without supplying energy from the outside can be achieved.
The temperature difference drive unit of the present invention can be applied to various electric devices such as, for instance, an electrically controlled mechanical clock. Since a battery is not required for driving thereof, the consumption of battery as a cause of environmental pollution can be reduced.